Hi All,
I am wondering why we should specify the use of the flow label as
part of the base IPv6 specifications at all. Why do we need
these rules as part of IPv6?
The flow label does not, by itself, provide any useful information
that a router can use to classify a flow and/or optimize packet
handling. In fact, without knowledge of a specific signalling
mechanism or flow-establishment mechanism, the router can't
use the flow label for anything at all. For example, a router
cannot use a flow label for QoS queuing or to optimize hop-by-hop
header processing, unless the router is aware of the signalling/
flow-establishment mechanism in use, since it will not
know the flow lifetime.
Any rules governing how the flow label is chosen, modified,
authenticated and/or interpreted will be specific to the
signalling/flow-establishment mechanism in use. And, all of
the nodes/routers that are utilizing one of these mechanisms
will be aware of the mechanism.
So why not specify the semantics/use/etc. of the flow label as
part of the signalling/flow establishment protocols?
The IPv6 specifications could merely include the current rule:
"Hosts or routers that do not support the functions of the Flow Label
field are required to set the field to zero when originating a packet,
pass the field on unchanged when forwarding a packet, and ignore the
field when receiving a packet." [from RFC 2460].
This rule should properly protect the flow label, so that
signalling/flow-establishment mechanisms can use the flow
label, as needed by the specific mechanism.
Margaret
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